The present invention relates to a method and an apparatus for controlling uniformly the width and the thickness of a descaled strip.
In a strip rolling process, edge drop (a thin portion) is unavoidably produced in widthwise edge portions of the strip. Accordingly, side trimming by rotary shearing is generally performed as an only means for removing the edge drop and to secure the desired dimensional accuracy in the width of the strip. However, this conventional side trimming had disadvantages such that a 1 to 2% loss in yield rate was usually unavoidable because the strip was cut away and discarded from both the edges to the depth of several millimeters to several tens millimeters and that the product after cold rolling became saw-toothed shape in the edges according to the shape of the sheared faces thereof, to thereby decrease the quality of the product.
As a means for overcoming the above-mentioned disadvantages, the inventors have developed a means for obtaining a strip of a desired thickness without performing side trimming by shearing, in which a descaled strip is corrected by reduction simultaneously in the widthwise and the thicknesswise directions on the exit side of a pickling line or on the entrance side of a tandem cold rolling mill (Japanese Patent Public Disclosure No. 160501/1982).
In the above-identified method, a strip which has edge drops on both the edge portions thereof and is not uniform in the width is corrected first by vertical rolls to define the width. At this time, the strip is somewhat bulged in edge portions thereof by reduction and tends to become dog-bone shape while, at the same time, horizontal rolls hold the strip to prevent its bending and shaking and urge the bulges in the edge portions toward the central portion to make the entire width of the strip uniform.
Further in said method, in order to prevent the width of the strip corrected at the time of defining the width from being affected at the time of vertical reduction, the reduction to correct the width of the strip and the reduction to correct the thickness thereof are performed at the same position or at slightly shifted positions approximately simultaneously. When a large amount of correction of the width or the thickness of the strip is requried, the step for said correction by reduction is provided at a plurality of successive positions to take suitable parts of the amount of correction, respectively, so that the strip corrected at the last position has the desired width or thickness.
The above-described control means in rolling is very effective in increasing the accuracy of the strip width without causing trimming loss. And, an inspection of the width of the strip rolled by this method shows that the width of the strip is controlled to the desired value over the substantially entire length thereof.
Increase in reduction during cold rolling of a strip tends to produce widthwise cracks in the edge portions of the strip. In order to prevent such cracks, accordingly, a shape correcting apparatus for processing particularly the edge portions of the strip during cold rolling was proposed (Japanese Patent Public Disclosure No. 109104/1981). In this apparatus, a pair of horizontal rolls spaced from each other in parallel and a vertical roll disposed in slight contact with the end faces of the horizontal rolls cooperate to define a caliber to thereby correct the shape of the edge portions of the strip. Said shape correcting apparatus is of such construction that the axes of the horizontal rolls are slightly inclined with respect to the widthwise direction of the strip (that is, the direction perpendicular to the direction of movement of the strip) so that the edge portions of the strip are squeezed into said caliber by the frictional force of the horizontal rolls.
The above-mentioned apparatus has, however, disadvantages such that the rolls are worn unduly by abrasion between the strip and the rolls and that the side face of the strip becomes out of flatness because metal flow caused in the direction of advancement of the strip according as the change in the sectional area of the strip produces bulging in the side face of the strip.
An object of the present invention is to provide a method and an apparatus for controlling reliably the width and the thickness of a strip.
Another object of the present invention is to provide a method and apparatus for controlling steadily the width and the thickness of a strip over the entire length including the top and the bottom thereof.